Kincella, I was a wood worker and table maker for many years,I think the best table is the extension table(would be keen to see a photo of the underneath)I think you'll find it is an Art Deco piece and I would guess the extension mechanism will be sliding parallel large running dovetails probably about 70mm x 50mm .The dark stain looks to me like an oil or grease stain,if so you may be able to get rid of it by pouring on metholated spirit ,let it soak in,steel wool it and then light it with a lighter,allow to burn a few minutes and then smother.Then steel wool the surface with the grain rather than across it. If the burning has worked (ie the stain seems lighter in colour just keep repeating the process)I think you may find the wood is teak When it comes to finishing it may I suggest an initial coat of shellac before you apply whatever other finish you wish to(I would recommend a classic oil resin finish hand rubbed)Make your mix using boiled linseed,gum turpentine and a little old fashioned varnish.Slowly heat the mix in a double saucepan (water underneath) until all components are blended well.Then remove from the heat and allow to cool.Later brush the mix on,leave overnight and steel wool the surface until it is smooth and there are no sticky bits. Buff it well with a balled up cotton or flannel cloth .Wait a few days and do it again,eventually you'll have a soft smooth glow as a finish and the finish will be in the wood not on the wood.When you touch it you will feel the wood not the finish. Good luck and enjoy the project
